STEMlab 125-14

Overview

The STEMlab 125-14 is the original Red Pitaya board, a versatile and compact measurement and control platform designed for a wide range of applications in electronics, signal processing, and embedded systems development. It features a dual-core ARM Cortex-A9 processor, an FPGA Xilinx Zynq 7010 SoC, and high-speed ADCs and DACs, making it suitable for tasks such as data acquisition, signal generation, and real-time processing.

Features

• 14-bit, 125 MS/s ADC and DAC

• Dual-core ARM Cortex-A9 processor

• FPGA Xilinx Zynq 7010 SoC

• 512 MB RAM

• 16 digital I/Os, 4 analog inputs, 4 analog outputs

• Multiple communication interfaces: I2C, SPI, UART, CAN

• Micro USB connectivity for power and console

• SATA daisy-chain connectors for multi-board synchronisation

Quick Reference

Category	Key Specifications
ADC	2 channels, 14-bit, 125 MS/s, DC-60 MHz
DAC	2 channels, 14-bit, 125 MS/s, DC-60 MHz
Processor	Dual-core ARM Cortex-A9
FPGA	Xilinx Zynq 7010 SoC
RAM	512 MB
Digital I/O	16 GPIOs @ 3.3V
Analog I/O	4 inputs (12-bit), 4 outputs (8-bit)
Connectivity	Ethernet, USB, Extension connectors

Board Layout & Pinout

The pinout diagram shows all external connectors including RF inputs/outputs (IN1, IN2, OUT1, OUT2) and extension connectors (E1, E2).

Technical Specifications

Parameter	Value	Units	Notes
Basic
Processor	Dual core ARM Cortex-A9	-
FPGA	FPGA AMD (Xilinx) Zynq 7010 SoC	-
RAM	512	MB	(4 Gb)
Core clock frequency	125	MHz
System memory	Micro SD up to 32 GB	-
Serial console connector	Micro USB	-
Power connector	Micro USB	-
Power consumption	5 V, 2 A	-	max
Connectivity
Ethernet	1	Gbit
USB	USB-A 2.0	-
Wi-Fi	Requires Wi-Fi dongle	-
RF inputs
RF input channels	2	-
Sampling rate	125	MS/s
ADC resolution	14	bit
Input impedance	1 MΩ / 10 pF	-
Full scale voltage range	±1 (LV) ±20 (HV)	V
Input coupling	DC	-
Absolute max. input voltage	±6 (LV) ±30 (HV)	V	DC values [1]
Input ESD protection	1500	V	DC
Overload protection	Protection diodes	-
Bandwidth	DC - 60	MHz
Connector type	SMA	-
RF outputs
RF output channels	2	-
Sampling rate	125	MS/s
DAC resolution	14	bit
Load impedance	50 Ω	-
Voltage range	±1	V
Output coupling	DC	-
Short circuit protection	Yes	-
Output slew rate	2 V / 10 ns	-
Bandwidth	DC - 60	MHz
Connector type	SMA	-
Extension connectors
Digital GPIOs	16	-
Digital voltage levels	3.3	V
Analog inputs	4	-
Analog input voltage range	0 - 7.0	V
Analog input resolution	12	bit
Analog input sampling rate	100	kS/s
Analog outputs	4	-
Analog output voltage range	0 - 1.8	V
Analog output resolution	8	bit
Analog output sampling rate	≲ 3.2	MS/s
Analog output bandwidth	≈ 160	kHz
Communication interfaces	I2C, SPI, UART, CAN	-
Available voltages	+5, +3.3, -3.4	V
External ADC clock	No	-	See [2]
Synchronisation
External trigger input	DIO0_P	-	E1 connector
External trigger input impedance	Hi-Z	-	Digital input
Trigger output	DIO0_N	-	E1 connector [3]
Daisy chain connectors (S1 & S2)	Yes	-
Daisy chain connectors speed	up to 500	Mb/s
Daisy chain connectors type	SATA	-
Ref. clock input	N/A	-
Ref. clock frequency	N/A	-
Ref. clock connector type	N/A	-
Boot options
SD card	Yes	-
QSPI	Not populated	-
eMMC	N/A	-
Environmental Specifications
Operating Temperature Range	0 to 55	℃	With default heatsink
Operating Humidity Range	< 90%	RH
Automatic Shutdown Temperature	85	℃
Dimensions
Size (L x W x H)	106.8 x 60.0 x 21.1	mm	See Schematics for details

Warning

Maximum Input Voltage

• LV mode: ±6 V absolute maximum

• HV mode: ±30 V absolute maximum

Exceeding these values may damage the board permanently.

See also

For more detailed information, please refer to the Original Gen board comparison table.

Performance & Measurements

You can find the measurements of the fast analog frontend here:

• Original Gen - STEMlab 125-14.

Schematics & 3D Models

Schematics

• Schematics_STEM_125-14_v1.1.pdf.

Note

Full hardware schematics for the Red Pitaya board are not available. Red Pitaya has open-source code but not open hardware schematics. Nonetheless, development schematics are available. This schematic will give you information about hardware configuration, FPGA pin connections, and similar.

Mechanical Specifications & 3D Models

• STEP 3D_STEM_125-14_v1.0.zip.

Hardware Details

Components

The STEMlab 125-14 uses high-performance analog components from Linear Technology (now Analog Devices) for the signal chain.

ADC: Analog Devices LTC2145-14

• Dual 14-bit, 125 MS/s ADC

• Low power consumption

• High dynamic range

DAC: Analog Devices AD9767

• Dual 14-bit, 125 MS/s DAC

• High SFDR performance

• Low power operation

FPGA: Xilinx Zynq 7010

• Dual-core ARM Cortex-A9 @ 667 MHz

• Programmable logic fabric

• Integrated peripherals and memory controllers

Oscillator: 125 MHz oscillator

• High-precision 125 MHz reference oscillator

DC-DC Converter: LTC3615

• High-efficiency step-down regulator

DDR3 SRAM: MT41J256M16HA-125

• 512 MB DDR3 RAM

QSPI Flash: S25FL128SAGNFI001

• Not populated on standard boards

Extension Connectors & Interfaces

Overview

The STEMlab 125-14 board features the following connectors and interfaces:

• E1 and E2 connectors: Primary expansion connectors with digital I/O, analog I/O, and communication interfaces. These connectors allow users to interface with additional hardware, sensors, or peripherals, enhancing the board’s capabilities.

• S1 and S2 connectors: Daisy-chain connectors for synchronising multiple Red Pitaya boards. These connectors enable clock and trigger synchronisation between boards.

Connector Physical Specifications

E1 and E2 Extension Connectors:

• Connector type: 2 x 13 pins IDC 2.54 mm pitch

• Pin count: 26 pins each (2x13 configuration)

• Pitch: 2.54 mm (0.1”)

Mating Connectors:

Note

When looking for mating connectors for custom Red Pitaya shields, double height elevated sockets are needed to clear the heatsink and ethernet connector on the board. Any connectors with insulation height of 0.635” (16.13 mm) or greater will work. This clearance requirement is based on the tallest components on the Red Pitaya board (heatsink and ethernet connector).

Note

To prevent damage to the board or the shield, when connecting shields to the E1 and E2 connectors, please ensure:

• Proper alignment of connectors - ensure the connectors are correctly aligned. The connectors on the Red Pitaya board have additional space in the socket housing, making it possible to misalign the shields by ±1 pin while still appearing physically connected. This can cause damage to the board and/or the shield, so please double-check the alignment before powering on the board.

• Tight-fitting counterparts - use connectors that fit securely to prevent accidental disconnections or damage.

E1 Connector - Digital I/O & CAN

The E1 extension connector provides digital I/O and CAN bus interfaces for control and communication applications.

Features:

• Two +3V3 power sources (max 0.5 A of current)

• 16 single-ended or 8 differential digital I/Os with 3.3 V logic levels

• Two CAN buses (configurable via software)

Electrical Specifications:

All DIOx_y pins are LVCMOS33, with the following absolute maximum ratings:

• Min. voltage: -0.40 V

• Max. voltage: 3.3 V + 0.55 V

• Drive strength: < 8 mA

E1 Pinout:

Pin	Description	FPGA pin number	FPGA pin description	Voltage levels
1	3V3
2	3V3
3	DIO0_P / EXT TRIG	G17	IO_L16P_T2_35	3.3V
4	DIO0_N / TRIG OUT	G18	IO_L16N_T2_35	3.3V
5	DIO1_P	H16	IO_L13P_T2_MRCC_35	3.3V
6	DIO1_N	H17	IO_L13N_T2_MRCC_35	3.3V
7	DIO2_P	J18	IO_L14P_T2_AD4P_SRCC_35	3.3V
8	DIO2_N	H18	IO_L14N_T2_AD4N_SRCC_35	3.3V
9	DIO3_P	K17	IO_L12P_T1_MRCC_35	3.3V
10	DIO3_N	K18	IO_L12N_T1_MRCC_35	3.3V
11	DIO4_P	L14	IO_L22P_T3_AD7P_35	3.3V
12	DIO4_N	L15	IO_L22N_T3_AD7N_35	3.3V
13	DIO5_P	L16	IO_L11P_T1_SRCC_35	3.3V
14	DIO5_N	L17	IO_L11N_T1_SRCC_35	3.3V
15	DIO6_P / CAN1_RX	K16	IO_L24P_T3_AD15P_35	3.3V
16	DIO6_N / CAN1_TX	J16	IO_L24N_T3_AD15N_35	3.3V
17	DIO7_P / CAN0_RX	M14	IO_L23P_T3_35	3.3V
18	DIO7_N / CAN0_TX	M15	IO_L23N_T3_35	3.3V
19	NC
20	NC
21	NC
22	NC
23	NC
24	NC
25	GND
26	GND

Note

To change the functionality of DIO6_P, DIO6_N, DIO7_P and DIO7_N from GPIO to CAN, please modify the housekeeping register value at address 0x34. For further details, please refer to the FPGA register section.

The change can also be performed with the appropriate SCPI or API command. Please refer to the CAN commands section for further details.

E2 Connector - Analog & Communication

The E2 extension connector provides analog I/O and communication interfaces for sensor integration and data acquisition.

Features:

• +5 V power source (max 0.5 A, shared with USB devices)

• -3.4 V/-4 V power source (max 0.1 A)

• SPI, UART, I2C communication interfaces

• 4 slow ADCs (12-bit, 100 kS/s)

• 4 slow DACs (8-bit PWM, ≲ 3.2 MS/s)

E2 Pinout:

Pin	Description	FPGA pin number	FPGA pin description	Voltage levels
1	+5V
2	-3.3V / -3.4V [4]
3	SPI (MOSI)	E9	PS_MIO10_500	3V3
4	SPI (MISO)	C6	PS_MIO11_500	3V3
5	SPI (SCK)	D9	PS_MIO12_500	3V3
6	SPI (CS)	E8	PS_MIO13_500	3V3
7	UART (TX)	D5	PS_MIO8_500	3V3
8	UART (RX)	B5	PS_MIO9_500	3V3
9	I2C (SCL)	B13	PS_MIO50_501	3V3
10	I2C (SDA)	B9	PS_MIO51_501	3V3
11	Ext com. mode (AIN)			GND (default)
12	GND
13	Analog Input 0	B19, A20	IO_L2P_T0_AD8P_35, IO_L2N_T0_AD8N_35	0-7.0 V
14	Analog Input 1	C20, B20	IO_L1P_T0_AD0P_35, IO_L1N_T0_AD0N_35	0-7.0 V
15	Analog Input 2	E17, D18	IO_L3P_T0_DQS_AD1P_35, IO_L3N_T0_DQS_AD1N_35	0-7.0 V
16	Analog Input 3	E18, E19	IO_L5P_T0_AD9P_35, IO_L5N_T0_AD9N_35	0-7.0 V
17	Analog Output 0	T10	IO_L1N_T0_34	0-1.8 V
18	Analog Output 1	T11	IO_L1P_T0_34	0-1.8 V
19	Analog Output 2	P15	IO_L24P_T3_34	0-1.8 V
20	Analog Output 3	U13	IO_L3P_T0_DQS_PUDC_B_34	0-1.8 V
21	GND
22	GND
23	NC
24	NC
25	GND
26	GND

Note

UART TX (PS_MIO08) is an output only. It must be connected to GND or left floating at power-up (no external pull-ups)!

Auxiliary Analog Inputs & Outputs

Auxiliary Analog Input Channels

The E2 connector provides 4 auxiliary analog inputs for slow-speed measurements and sensor interfacing.

Parameter	Value	Units	Notes
Number of channels	4	-
ADC resolution	12	bit
Sampling rate	100	kS/s	[5]
Input voltage range	0 - 7.0	V
Input coupling	DC	-
Connector	Extension connector E2 connector	-	Pins 13, 14, 15, 16

Auxiliary Analog Output Channels

The E2 connector provides 4 auxiliary analog outputs using PWM with low-pass filtering.

Parameter	Value	Units	Notes
Number of channels	4	-
Output resolution	8	bit
Sampling rate	≲ 3.2	MS/s
Output bandwidth	≈ 160	kHz
Output voltage range	0 - 1.8	V
Output coupling	DC	-
Output type	Low pass filtered PWM	-	[6]
PWM time resolution	8	ns	(1/125 MHz)
Connector	Extension connector E2 connector	-	Pins 17, 18, 19, 20

General Purpose Digital I/O Channels

Parameter	Value	Units	Notes
Number of GPIOs	16	-
Digital voltage level	3.3	V
Abs. min. voltage	-0.40	V
Abs. max. voltage	3.3 + 0.55	V
Current limitation	< 8	mA	Drive strength
Direction	Configurable	-
Time resolution	8	ns	(1/125 MHz)
Connector location	Extension connector E1 connector	-

Synchronisation Connectors (S1 & S2)

The Original generation Red Pitaya boards feature SATA connectors for multi-board synchronisation (daisy-chaining).

Synchronisation Connectors:

Parameter	Specification
Connector type	SATA
Number of connectors	2 (for daisy-chaining)
Maximum data rate	up to 500 Mb/s
Purpose	Clock and trigger sync

Note

The SATA connectors are meant to be used for synchronising multiple Red Pitaya boards. They are not compatible with standard SATA storage devices (voltage levels are 1V8), so extra care must be taken when connecting external devices to these connectors to avoid damaging the board.

Note

For multi-board synchronisation, the secondary boards require hardware modification (resistor relocation: R25, R26 → R27, R28) to receive the clock signal through the SATA connectors. Please refer to the External ADC Clock section for more information.

See also

• X-channel system specifications - Multi-channel system details

• X-channel 2.0 (Click Shield) synchronisation - Alternative synchronisation method for Original and Gen 2 boards

• Multi-board synchronisation examples - Software examples

Advanced Features

Power Supply

Red Pitaya boards can be powered through two methods:

1. Micro USB connector

2. +5V pin (pin 1) and GND pin (pin 25, 26) on the |E2| connector

Power Supply Specifications:

Parameter	Specification
Power supply voltage	5 V
Maximum current draw	2.0 A
Power supply type	DC

Note

The board’s maximum current draw is 2.0 A. The power supply may have a higher current rating — this will not cause any issues.

The micro-USB power input includes a simple integrated protection circuit that prevents damage to the board.

Figure 4.4 Protection circuit for powering through the micro-USB connector

Warning

When powering the Red Pitaya through the extension connector (+5V pin on E2 connector), external protection must be provided by the user to protect the board from overvoltage and overcurrent conditions.

Available Power Rails on Extension Connectors:

The E1 connector and E2 connector connectors expose several power rails that can be used to supply power to external devices or circuits connected to the board. The current limits below are the maximum currents that Red Pitaya can source from each rail to external loads — they are not related to the board’s own power consumption.

Voltage Rail	Max. Sourceable Current
+5 V	0.5 A [7]
+3V3	0.5 A [7]
-3.3V / -3.4V / -4 V	0.05 A

Note

Exceeding these limits may cause voltage rail instability, which can result in a board reset or shutdown.

External ADC Clock

Note

The standard STEMlab 125-14 does not support external ADC clock without hardware modification. If you need external clock support without modification, consider these pre-modified boards:

• STEMlab 125-14 External Clock - Board with external clock capability

• STEMlab 125-14 4-Input - Board with 4 input channels and external clock capability

Clock Sources

The ADC clock can be provided from three sources:

• On-board 125 MHz oscillator (default): Internal clock source

• External source through E2 connector: External clock via Ext. ADC Clk± pins (requires hardware modification: R25, R26 → R23, R24)

• SATA connectors (from FPGA): For X-channel secondary/slave configuration (requires hardware modification: R25, R26 → R27, R28)

Figure 4.5 Clock source options for the ADC

External Clock Specifications

The external ADC clock should be a differential LVDS signal:

Parameter		Description	Min	Typ	Max	Unit
	Clock input pins	23 (Clk+) and 24 (Clk-) on E2 connector
	Input standards	LVDS
	Input clock coupling	AC (on-board capacitors)
\(f_{CLK}\)	Input frequency range		1	125	125	MHz
\(V_{ID,DIFF,PP}\)	Input voltage swing	Differential peak-to-peak		0.35	0.8	V
IDC	Input clock duty cycle		45%		55%

Hardware Modification Instructions

To enable external clock input, SMD resistors must be relocated on the PCB:

1. Remove R25 and R26 from the top side of the board

   

   Figure 4.6 Top side schematic

2. Relocate the desoldered resistors from R25 and R26 to:

   • R23 and R24 for external clock (Ext. ADC CLK± pins on E2 connector)

   • R27 and R28 for X-channel secondary (SATA connectors)

   

   Figure 4.7 Bottom side photo showing the location of the resistors

   

   Figure 4.8 Full schematic with highlighted resistor positions

Warning

Changing the external clock frequency during operation is not supported

The Red Pitaya FPGA is designed, tested, and guaranteed to operate correctly at 125 MHz.

While it is possible to run the board at different clock frequencies, please be aware that:

• The FPGA may not function as intended at non-standard frequencies and requires thorough testing

• The ADC and DAC sampling rates will change proportionally with the clock frequency

• Lower clock frequencies will reduce the analog bandwidth of the board

• Red Pitaya does not guarantee proper operation at frequencies other than 125 MHz

The board will boot with any valid external clock signal. OS versions 2.07-48 and higher do not block boot-up if the external clock is absent.

Warning

Any non-Red Pitaya hardware modification will void the warranty, and we cannot guarantee support for modified boards.

QSPI Flash

The QSPI flash chip is by default not populated on Red Pitaya boards. For further information on board modifications, please contact support@redpitaya.com or info@redpitaya.com.

Warning

Any non-Red Pitaya hardware modification will void the warranty, and we cannot guarantee support for modified boards.

Calibration

Red Pitaya original generation boards are factory-calibrated. Recalibration may be required after extended use, environmental changes, or when measurement accuracy degrades.

There are three ways to calibrate the board:

• Calibration application — graphical interface accessible from the System Tools menu. Recommended for most users.

• Calibration command line utility (calib) — command line tool for scripted or advanced calibration workflows.

• C++ or Python API commands — programmatic access to calibration parameters.

For a full description of the calibration procedure, required equipment, and technical reference, please refer to the Calibration documentation.

Note

Original generation boards require 50 Ω terminators during calibration due to a mismatch in the impedance of fast analog inputs and outputs.

Additional Resources

For additional specifications and measurements, please refer to:

• Original Gen hardware specifications - Common Original Gen specifications

• Original Gen board comparison table - Comparison across all Red Pitaya Original Gen models

Legal & Disclaimers

Note

The information provided by Red Pitaya d.o.o. is believed to be accurate and reliable. However, no liability is accepted for its use. Please note that the contents may be subject to change without prior notice.

Footnotes

[1]

The absolute maximum input voltage values are for frequencies below 1 kHz. For higher frequencies, please use the input voltage range specifications as Absolute maximum.

[2]

See the STEMlab 125-14 External Clock board for more information, or refer to the External ADC Clock section for hardware modification instructions.

[3]

See the X-channel 2.0 (Click Shield) synchronisation and X-channel 2.0 (Click Shield) synchronisation examples for trigger output configuration.

[4]

Red Pitaya Version 1.0 has -3.3 V on pin 2. Red Pitaya Version 1.1 has -3.4 V on pin 2.

[5]

The default software enables sampling at a CPU-dependent speed. To acquire data at a 100 kS/s rate, additional FPGA processing must be implemented.

[6]

The output is passed through a first-order low-pass filter. Should additional filtering be required, this can be applied externally in line with the specific requirements of the application.

[7] (1,2)

Application specific. The output current is shared between the extension connectors and the connected USB devices, and can be higher if other peripheral units are not in use.